The present invention relates to continuous form printers, and more specifically to a tractor feed control system used in such printers.
Printers using fanfold continuous paper are well known. Tractor feeding is conventionally used because it provides simple feeding at a standard feed interval (conventionally 1/2") without paper alignment and guiding problems associated with cut sheets. Typically, the standard feed interval corresponds to the distance between successive tractor feed holes of standard paper (hole pitch), and feed control systems generate a pulse signal for every hole pitch interval. A conventional printer of this type only able to use a continuous paper with a page length being a multiple of the standard feed hole pitch. In this case, perforations for separating one page of the fanfold sheet from the next page are positioned between feed holes at the same relative position for each page.
However, such a printer is not able to use papers having different paper advance intervals, where the paper advance amount does not correspond to the feed hole pitch. For example, one may want to use a continuous sheet printed with a standard form having text entry blanks at 3/8" spacing, thus requiring a paper advance of 3/8" or 1/8". Furthermore, there is no way of providing parts or adjusting a conventional printer to be able to handle page lengths that are not multiples of the standard feed hole pitch, where perforations (separating pages) may be in different locations in relation to the nearest feed hole for successive pages, and may even intersect a feed hole. For example, if one uses a continuous sheet having pages with a length of 105/6 inches and a feed hole pitch of 1/2", the leading edge of each page will be in a different position relative to the nearest feed hole. In this case, it is impossible to use the feed holes alone to define the leading edge of the paper, as the distance from the leading edge to the closest feed hole varies between pages.
For these reasons there exists a need for a continuous form printer that is able to feed paper using multiple feed intervals without undue adjustment or the changing of parts, and which can automatically register pages of different lengths and corresponding feed intervals.